Illumination systems for illuminating display devices are known per se. They are used, inter alia, as backlighting systems in non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are used in, for example, television receivers, (computer) monitors, (cordless) telephones and PDAs. These illumination systems can also be used in, for example, projection systems such as a digital projectors, also referred to as beamers, for projecting images or displaying television programs, films, video programs or DVDs, or the like.
To reduce motion blur in display devices, the known illumination systems comprise an array of light sources which can be operated in a scanning backlight mode of operation. To enable the scanning backlight mode, the array of light sources in the known illumination system is segmented so as to enable parts of the display to be illuminated selectively. Alternatively, selective illumination may be used in the known illumination systems, for example, in a dimmable backlight mode of operation so as to enhance the contrast of the display device. The luminance of each particular light source in the array of light sources may be adapted (for example, dimmed), depending on a luminance content of a part of the image illuminated by the particular light source.
US 2004/0174706 discloses an optical illumination system with which a direction of emission of the light emitted by light-emitting devices can be influenced. The optical system comprises a plurality of light-emitting devices which have a wide beam spread and are spatially arranged in an array. An embodiment of the optical system includes a plurality of horizontal planar reflective optics arranged adjacent to the rows of light-emitting devices. The horizontal reflective optics provide a moderate off-axis distribution of the illumination in a vertical direction and a wide beam spread in a horizontal direction. In this way, the known illumination system is segmented so as to selectively illuminate part of the display.
The known illumination system has the drawback that the reflective optics typically cause brightness differences within the segmented area.